The proposed work will examine the mechanisms by which peptide hormones and metal ions control adenylate cyclase activity. Most of the proposed work will focus on the control of adrenal adenylate cyclase by ACTH and calcium ion. New ACTH analogs suitable for radiolabeling without loss of biological activity are being sought. Additional studies are planned to investigate the control of adenylate cyclase activity in normal parathyroid glands, parathyroid adenomas and a transplantable rat medullary thyroid carcinoma.